Digester control



Jul '29, 1941. ANNlN. 2,251,246 DIGE-STER CONTROL Filed Oct. 19, 1938 FIG. I. 4

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u '28 :0 l I n 3o 3 I; I j w as I9 LINE 3o 7 INVENTOR.- IO i DOUGLAS H.ANNIN 3 ATTORNEY Patented. July 29, 1941 UNITED STATES PATENT OFFICE I 2,251,246 DIGESTEB. oomol. Douglas H. Annin, San Francisco, Calif., assignor to The Brown Instrument Company, Philadelphia, Pa a corporation of Pennsylvania Application October 19, 1938, Serial No. 235,743

claims. (01. 236546) The present invention relates to a. process of digesting wood chips in a suitable digester to procure pulp and, more particularly, to a manner of supplying steam 'to the digester to make the cooking process proceed according to a predetermined schedule.

The usual process of cooking chemical pulp consists of putting chips and suitable chemicals in a digester, tightly closing the same, and introducing steam into the 'digester to carry out the cooking process. The addition of heat produces a chemical reaction in the charge which separates the cellulose from the lignin, pitch, etc. and effects the so-called digesting process. The maintenance of a schedule of temperature in the di- ,gester during the cooking is of primary importance since, if the temperature is too high, the acid used in the process attacks the cellulose, destroying some of it; and if the temperature is too low; it takes an unnecessarily long time for the process to be carried out. It is customary to gradually raise the temperature'by admitting increasingly large quantities, of steam until the process is well under way, and then lower the quantity of steam introduced as the cooking process nears its end. A

My invention is specifically directed to a method and apparatus for introducing steam into-a digester in accordance with the temperature therein and in accordance with apredetermined time schedule. To this end, I provide a flow controller to control the opening of a steam admission valve and reset the point at which the flow controller tends to keep the valve by an instrument which is responsive to the temperature of the digester and a predetermined time schedule.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. Fora better understanding of the invention, however, its advantages and specific objects obtained with its use, reference should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

in the drawing:

Fig. 1 is a diagrammatic representation of a digester and the arrangement of instruments used .to control'ityand Fig. 2 is a detailed view of one type of flow and temperature control instruments that may be used. r

Referring first to Fig. 1, there is shown a digester I which is filled with chips and chemicals to be later described.

As the cooking of the chips progresses, a pressure is built up in the top of the digester by the increase in volume of the charge due to theaddition of steam, and also by the accumulation of sulphur-dioxide gas that is liberated as a result of the cooking. It is the usual practice to permit this gas to accumulate until it has reached some predetermined pressure, at which time a relief Valve is automatically opened. To this end, a

pressure controllerv 5 which is responsive to the pressure in the top of the. digester is used to.

regulate the pressure of air supplied through line B to-the diaphragm of an air actuated valve I in a relief line 8. The particular type of pressure controller forms no part of my invention and it is sufiicient to state here that the one herein shown at 5 is represented as being a Brown air operated recording pressure controller.

' The steam supply, line 3 is provided with an orifice 9, from the opposite sides of which pressure taps l0 and II are taken tothe legs of a U-tube manometer l2. As the flow through the line 3 varies, the level of the liquid, such as mercury, in the manometer will vary the height of a float l3 therein, which float has attached to it an armature II that moves in inductive relation with a pair of induction coils IS in the manometer. These coils are electrically connected by a cable Hi to a similar pair of coils I! in a flow meter I8, which connection is such that as the flow through the line 3 increases and the float I3 is lowered, a core l9 in inductive relation with the coils II will be raised. The upper part of the core l9 isattached to one arm of bell-crank lever 20, pivoted at 2|. The second arm of the bell-crank 20 is connected by a. link 22 to one arm of a bell-crank 23 pivoted at 24, the other arm of which is connected by a link 25. to one end of floating lever 26 whose fulcrum is normally provided by the lower end of a'shiftable link 21. The arrangement is such that as the fl ow increases, the link 22 will be moved to the right, and the left end of lever 26 will belowered.

Movement of .this lever is used to adjust the air pressure applied to a diaphragm in valve 4,

which valve may be of the type that is opened by a spring and closed by the pressure of the air applied to its diaphragm. A supply of air under suitable pressure for the valve leads from a supply line 28 through a restriction 29 and a line 30 to the valve. A branch line 3| leading from theline 30 opens into a chamber'32 which is formed between a cap 33 and a bellows 34, both of which are rigidly attached to a Support 35. A bleed nozzle 36 connected with the chamber 32 is variably throttled by a flapper valve 38 in such a manner that as the valve is moved from the nozzle, air can escape through it faster than it can through the restriction 29 and thereby relieve the pressure on the diaphragm of the valve 4, so that the valve can open. As the flapper valve 38 is moved towards the nozzle to restrict the flow therethrough, pressure will be built up in the lines 30 and 3|, and the valve 4 will be closed. The flapper valve 38 is pivoted on a support 39 extending from the support 35 and is acted upon by a pin 40 on one end of a bellcrank 4| which is pivoted on a rod 42 attached to the inner end of the bellows 34. The other arm of the bell-crank 4| is-pivoted at 31 to the center of the floating lever 26.

The operation of this instrument is as follows. When the flow increases, the left end of lever 26 is lowered by the linkage above described, thus causing the pin 40 to be moved to the right, allowing flapper 38 to restrict the escape of air through nozzle 36 and thereby increasing the pressure on its diaphragm to close the valve. A

follow-up motion is provided to prevent overtravel of the valve by means of the-rod 42 to which the bell-crank 4| is pivoted. As the pressure in chamber 32 increases due to restricting the flow through nozzle 36, the bellows 34 will collapse and move the bell-crank 4| to the left so that the pin 48 can move the flapper 38 away from the nozzle 36 to a distance slightly closer to the nozzle than it was before the change in flow.

I desire to change the point at which the instrument |8 will control thefiow through the line 3 in response to the temperature in the digester and in response to a predetermined time cycle, and to that end provide means for adjusting the control point of the instrument in response to the temperature. Such a means consists :of bellcrank 43 which is also pivoted at 24 and has one arm attached to the upper end of link 21 and the other arm attached to the link 44 which connects with the left end of bellows 45 that is expanded or contracted in response to changes in pressure. The expansion of the bellows 45 will raise the link 21 and thereby raise the control point of this instrument, inasmuch as the armature l9 will then have to be raised a greater amount in order for the flapper 38 to be moved within the same distance of the nozzle 36.

The means by which bellows 45 can be expanded and contracted consists of a temperature controlling instrument 54 that is similar in most respects to the instrument Hi just described. Air is supplied under suitable pressure from a source 46, which is shown as being the same source that supplies line 28, through a restriction 41 to a line 43 leading to the stationary end of bellows 45. A branch line 49 leads from the line 48 to a chamber 32A, similar to chamber 32, so that as the pressure in the chamber 32A is varied, the pressure in the bellows 45 will be correspondingly varied to lengthen or contract it. A lever system similarto that in the instrument 3 is pro- '75 vided for moving a flapper 38A with respect to a nozzle 36A to vary the pressure in chamber 32A. In this instrument, however, the link 22A is moved by' a lever 49, pivoted at 53, which is in turn moved in response to the expansion and contraction of a helix 5| that is connected by a capillary tube 52 with a temperature responsive bulb 53 located in the digester. As the temperature in'the digester is increased, the helix 5| will unwind and move lever 43 clockwise around 50, shift link 22A to the left, and raise the left end of lever 26A to move the flapper 38A away from the nozzle 36A. This will permit more air to escape through nozzle 36A to reduce the pressure in. chamber 32A and bellows 45, and thereby lower the control point of the instrument la. The control point of this temperature responsive instrument 54 is changed according to a predetermined time schedule by moving the bell-crank 43A and link 21A in response to a predetermined time cycle as set by a cam 55. This cam is shaped to conform to the schedule it is desired to maintain in the digester and is rotated at a constant speed by constant speed motor M, as diagrammatically shown, and as it rotates, raises and lowers a roller 56 on the end of one arm of a bell-crank 51 that is pivoted to a lever Movement; of the bell-crank 51 shifts the link 44A axially to change the control point of the instrument 54 in a manner described in connection with the shifting of link 44 in the instrument N. The lever 58 may also be moved by hand if desired by the knob 53 in order to initially set the control point of this instrument or to change it manually during the cooking process.

The operation of the system as a whole will now be described. When the digester has been charged and closed, steam will be admitted thereto through the steam line 3 at a rate determined by the flow controlling instrument l8. As the digesting process proceeds, the temperature in the digester will build up as will the pressure, which latter is relieved through line 8 and valve I under the control of the instrument 5. Changes in temperature in the digester, along with the time that the process has been carried on, as determined by the cam 55, will vary the air pressure in bellows 45 and change its length. This change in length of the bellows 45 will alter the control point of the flow controller so that the supply of steam to the digester will be Varied in response to its temperature and the time that the cook has been in progress. In this manner, a predetermined schedule of the operation of the digester may be obtained, which schedule can be automatic, as necessary, or manual, if desired, in accordance with the temperature conditions in the digester. proceed atthe optimum rate and insures better quality of pulp than is possible by previous methods, or by a cook that has been manually controlled.

It will be obvious that other instruments capable of performing the same functions as those herein described may be used if desired. My invention relates to the novel method of and arrangement of apparatus for controlling ,the supply of steam to a digester, and therefore the digestion process, rather than to the specific" details of any apparatus by which it may be done.

While in accordance with the provisions of the statutes, I have illustrated and described the best form of embodiment of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the This permits the cooking to.

form of the apparatus disclosed without departing from the spirit of my invention as set forth in the appended claims, and that certain features of my invention may sometimes be used to advantage without a corresponding use of other features.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. Digester control apparatus comprising in combination with a digester, a steam line leading thereto, a valve in said line, a flow control apparatus to regulate said valve, said apparatus having a controlpoint adjustment, a temperature responsive apparatus responsive to the temperature in the digester to adjust the control point of the flow control apparatus, and means to regulate said temperature responsive apparatus in accordance with a predetermined schedule.

2. Digester control apparatus comprising in combination a digester, a steam supply line therefor. a valve in said line, means to control the opening of said valve in response to rate of flow of the steam therethrough, and means to adjust said flow controlling means in response to the temperature within the digester and a time schedule.

3. Digester control apparatus comprising in combination a digester, a supply line leading thereto, a valve in said line, apparatus responsive to the flow of a fluid through said line to adjust said valve, a device responsive to the temperature in the digester, means actuated by said device to adjust said flow controlling apparatus, and a time cycle means to adjust said temperature responsive device.

4. The method of controlling a digesting process which comprises supplying steam to a digester at a given rate of flow and directly varying said rate of flow in accordance with the temperature of the digester and a predetermined time schedule to maintain desired temperature conditions in the digester during desired periods of time.

5. Digester control apparatus comprising in combination with a digester a steam line leading thereto, valve means in said steam line for regulating the supply of steam to the digester, control means responsive to the rate of flow of steam to the digester, control means responsive to the temperature of the digester, time operated control means responsive to a predetermined time schedule, and means controlled by the conjoint action of said control means for operating said valve means to regulate the supply of steam to the digester to maintain desired temperature conditions in the digester during desired periods of time.

. DOUGLAS H. ANNIN. 

